Updating Bug

I recently recieved the latest model of the 11" Macbook Air, with OS X Mavericks installed out of the box. Mac App Store Version 1.3 is the program with which I am having difficulties. When I first open the "Updates" tab, it displays the correct size of the update in megabytes, but when I click on the "Update" button, my computer proceeds to re-download the entire application! This uses gigabytes of internet and hours of my time, incapacitating whatever application is being "updated" for long periods of time. Of course, adding insult to injury is the fact that there is no easy way to cancel updates and my internet, optimistically, goes about 200-300 KB/sec (at worst only about 80 KB/sec). I don't expect any help with the internet situation, but I would like to know how to do something about this, or if Apple is aware and addressing the problem.